It is known to construct articulatable beds which can be convertible to a chair position and this is particularly so with respect to hospital beds. For example, such a bed is described in U.S. Pat. No. 6,427,264. Reference is also made to U.S. Pat. No. 6,141,806 which relates to a bariatric bed and in both these patents the leg section of the bed is compressible by removing air from an extendible cushion. When the bed is moved to a seating position it is necessary to compress the leg rest section and this is achieved by providing an inflatable bag which is restrained and which is extendible by pumping air in the bag and compressible by releasing air from the bag. Such extendible leg rest sections have not functioned adequately and are problematic. For example, they require an air compressor and control devices for admitting and releasing air from the inflatable bag. This equipment is costly and requires extra space for mounting under the bed. It is also noisy. Also, the bag does not provide a solid support surface as any load on the bag displaces air and makes the support surface unstable. These bags can also be punctured and they don't offer safety features which are paramount with hospital beds. These bags also often need to be adjusted by an operator. With this type of bed construction it is not possible to provide a mattress wherein all the mattress sections are located in a single fabric envelope, due to the compression of the inflatable bag when air is released.